1. Field of the Invention
The invention concerns a snap-in locking device for a multistage rotary switch with a switch spindle that is connectable with a rotary knob, by means of which a switch part is adjustable into several switch positions, wherein the switch positions are determined by the pre-defined snap-in positions of the snap-in locking device, which comprises a snap-in lock element and counter-snap-in elements.
2. Description of the Related Art
Rotary switches of different constructions are used in a variety of electric devices. Subsequently, the rotary switches may feature different switch positions that can be set by rotating the switch spindle in one or another direction. The number of switch positions may also vary and cover the entire angular range of 360xc2x0 degrees or just a part thereof.
Rotary switches that are installed into a housing are frequently designed as a complete component, as disclosed in DE 94 19 356 U1, DE 31 40 772 C2 and DE 37 40 415 A1.
Rotary switchers are also being used more and more as operating units for household appliances for transferring control signals to a corresponding electronic device control. Consider program selection in washing machines, dishwashing machines or microwave appliances for a moment.
As disclosed in DE 31 15 358 C2 such operating units are constructed from several components, each of which fulfill separate sub-tasks. The snap-in locking device for such an operating unit, i.e. rotary switches, constitutes an essential component that requires considerable parts and labor expense, in particular in conjunction with the other components of the operating unit, like the rotary knob for adjusting the switch spindle, limit stops for setting the number of switch positions and the actual switch or control part.
The task of the invention is to create a snap-in locking device for a multistage rotary switch as a component of the type mentioned at the outset, that can be realized with little cost and labor expenditure, easily configured to a variety of switch positions and easily connected with the other components in an operating unit.
According to the invention this task is solved in that the switch spindle is connected with an axle part that is snapped into an inner receptacle of a built-in switch panel part, that the axle part rests on the switch panel part and is lock-in adjustable between snap-in receptacles with cams that are each limited by two radially-aligned connector links, that the snap-in receptacles extend around the entire circumference of the inner receptacle of the switch panel part, that the axle part can be set into rotary motion with the switch spindle by means of a rotary knob, which is attachable to the switch spindle, and that modifiable limit stops define the number of switch positions.
The switch spindle with the axle part is snapped directly into a switch panel part as is desirable in household appliances with program selectors. The switch panel part may be used as a counter-snap-in element for several program selectors. Preferably, the switch spindle forms a one-piece plastic-injection mould part with the axle part and can be mounted rotatable in the switch panel part without separate fastening parts. The connector links form snap-in receptacles into which cams as snap-in elements of the axle part are snapped.
The design of the switch spindle as a flexible shaft provides a tolerance offset to the rotary switch of a control unit, as well as seamless fit of the control unit into the switch panel and/or operating screen part. This type of decoupling the snap-in locking device to the control unit primarily enables a flexible and cost-efficient design of the operating unit without the snap-in mechanisms.
At the same time it can be a benefit that the front and back edges of the cams are beveled so that the switch spindle with the axle part can carry out the necessary axial positioning movements in the inner receptacle of the switch panel part from switch position to switch position without undoing the snap-in connections between the axle part and the switch panel part. The rotary knob is simply slipped on to the non-circular switch spindle and fastened. The snap-in locking device with switch spindle and axle part as well as rotary knob and switch panel part can be mounted easily and quickly without separate fastening parts. The non-circular switch spindle is easily coupleable with the other function parts of the operating unit via a flexible shaft that provides a tolerance offset.
One design for the snap-in connection between the axle part and the switch panel part provides that the axle part features a collar that is segmented into snap-in tabs with catch stops on the outside that can be snapped into the inner receptacle of the switch panel part.
A further provision is that the inner receptacle of the switch panel part provides a localization receptacle and that a snap-in of the axle part provides a locating catch for correct snap-in positioning of the axle part with the switch panel part and for alignment with limit stops of the switch panel part and limitation of the switch positions; it is then ensured upon assemblage that the axle part and the switch panel part will assume a defined angle position from which adjustment of the switch positions is possible, which is limited by the limit stops.
A provision in another embodiment is that the axle part is likewise designed as a plastic-injection mould with the switch spindle and unlike the switch panel part, which consists of the copolymer Acrylonitrile Butadiene Styrene (ABS), is made of a polymer polyoxymethylene (POM). In doing so, optimal spring characteristics can be apportioned to the flexible shaft. Such a varied material selection also contributes to friction reduction since only these two parts carry out a rubbing movement against each other.
The connection between the rotary knob and the switch spindle is maintained simply in that at least the front section of the switch spindle that protrudes out from the switch panel part has a non-circular profile and that the rotary knob, which can be slipped-on, features a notched tab receptacle for engagement with the front section. Additionally, the hold of the rotary knob on the switch spindle can be improved in that the notched tab receptacle of the rotary knob is held on snug-fit or press-fit onto the front section of the axle part by means of a notched annular spring or the like. Irrespectively, an over-rotation safeguard can be achieved by such localization of the rotary knob on the switch spindle without spoiling the parts of the snap-in locking device, if the rotary knob is rotated further with a great amount of power when limiting the rotation of the axle part.
By more or less clearing snap-in receptacles, i.e. shifting the limit stops, the number of axle part switch positions in the switch panel part can be modified. This can be done easily by modifying the positions of the limit stops when the switch panel part is being manufactured. Modification costs for the injection moulds are also minimal. If the snap-in receptacles are separated at a distance of 30xc2x0 by two connector links, then the snap-in locking devices can be produced with up to 12 switch positions. Manufacturing costs for these parts are low since they can be produced completely automatically.
One arrangement provides for aesthetic reasons that the switch panel part bears on the front side a circular cavity around the inner receptacle for receiving the rotary knob and that the axle part rests on the backside of the switch panel part. A large part of the rotary knob is sunken into the cavity, nonetheless remaining well within grasp, but does not stick out far from the switch panel. In this arrangement the rotary knob and the switch panel part cover all the function elements of the snap-in locking device.
The procedure for installing the remaining components of the operating unit according to one arrangement is to make the front section of the switch spindle, which is formed on the side of the axle part facing away from the switch panel part, coupleable with a rotatable switch part of an electric switch coordinated to the intervals of the switch positions of the snap-in locking device and mounted on the preferably non-circular section of the switch spindle and mounted rotatable in a switch part built into the switch panel, or that this section of the switch spindle that is formed on the side of the axle part facing away from the switch panel part bears an electric or electronic control unit. The control unit mounted on the flexible shaft section can be roughly placed, i.e. tolerance-sensitive.